It's a sad state of affairs if people don't at least try to do something In 1 sided attacks when there's other people around them to back you up. I think it'd be harder to stand back and do nothing than at least trying to reason verbally with the offender if you don't fancy your chances of pulling someone off someone being attacked.
Doesn't mean i'll take too kindly to someone smaller than me threatening me though and i'll tell em in no uncertain terms

So I do realise how some of these things actually start and that's why it's difficult to assess what you're seeing in most of the town centre scuffles.
I lost my hearing in one ear for a few weeks about 6 or 7 years ago after sorting out some cnut that was battering a girl one night and making the mistake of walking off with my back to him after I thought i'd beaten him then he ran up behind me and punched me in the ear rupturing my eardrum, before running off

I did question my logic when my ears were so unbalanced it was causing me no end of problems and I was worried my ear would never recover
If only people fought fairly using schoolyard rules. No head kicking, no punching from behind and no weapons.